Signal barrier



Jan. 25, 1966 w ALLGAIER 3,231,778

S IGNAL BARRIER Filed June 20, 1963 INVENTOR Wi/l/am A. Aflga/er ATTORNEY oscillation near the end of the retrace. then radiated from the high voltage rectifier tube and is United States Patent f 3,231,778 SIGNAL BARRIER William A. Allgaier, Emporium, Pa., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed June 20, 1963, Ser. No. 289,369 3 Claims. (Cl. 313-313) This invention relates to electron discharge devices and more particularly to electron tubes adapted for use in high voltage rectifier applications.

Electron bombardment and rapid deterioration of glass envelopes resulting in catastrophic failures is well known in electron tubes of the rectifier type operated in high voltage applications. Further, radiated signals generated by the above-mentioned electron bombardment which are amplified and appear as undesired distortion in the output of a device such as a television set are also well known to those who manufacture tubes and service equip ment wherein such tubes are used.

Over the years, the combination of increased values of applied voltage, increased circuit efiiciencies, and increased compactness of design has repeatedly brought with it the reappearance of undesired signal radiation. In television sets, this radiated signal is often referred to as diodehausen and appears as a band on the left side of the picture tube.

This phenomena is believed to be an RF multiple frequency component combined with a very soft X-ray of about 120 angstroms. The X-rays are emitted from the shield surface while the RF signal originates in the sweep circuit and is caused by the high voltage spike in the flyback circuitshocking the circuit into multiple frequency This signal is amplified by the circuitry of the set until it appears as a highly undesirable and unwanted visual defect on the picture tube of the television set.

The problem is not new and has been previously alleviated in a number of ways which, unfortunately, were not permanent. Probably the most effective and least expensive technique has been the various methods of treating the glass envelope of the high volt-age rectifier tu-bes.

At first, the lime glass envelope of the tube was replaced with a lead glass envelope which reduced the problem but greatly increased the cost of tube manufacture. Upon reappearance of the radiated signal, a lime glass envelope was coated on the inner surface thereof with a layer of lea-d. Again, the problem was reduced and the cost of tube manufacture increased because of the increased handling and required processing of the envelopes. As applied voltage-s increased, a layer of lead was deposited upon a designated portion of the envelope inner surface and temporary relief from the problem was obtained.

Once again, applied voltage values, circuitry efiiciency, and design compactness have been improved an diodehausen has reappeared in many of the latest model television sets. Further, available and known electron tubes adapted for use as high voltage rectifiers are no longer adequate in preventing this phenomena in a number of these models. Moreover, it has been found that the metal of the film, the location of the film, and known methods of depositing the film leave much to be desired with regard to manufacturing cost, automation, high voltage arcing, and electron emission of the tube initially as .well as after extended periods of operational use.

Therefore, it is an object of this invention to enhance the barrier to signals radiated from an electron tube adapted for use in high voltage applications.

Another object of the invention is to improve the barrier to electron bombardment of a glass envelope for an ice electron discharge device adapted for use in high voltage applications.

Still another object of the invention is to reduce deleterious effects of electron bombardment in an electron discharge device having a glass envelope without adverse effect upon the electrical characteristics of the device.

A further object of the invention is to economically improve and automate the process for providing a barrier to signal radiation and envelope deterioration of an electron discharge device having a glass envelope and adapted for use in high voltage applications.

A still further object of the invention is to provide a process which enhances the electrical characteristics of an electron discharge device having a glass envelope and a high voltage gradient between electrodes therein.

Briefly, these object are fulfilled in one aspect of the invention by the provision of an electron discharge device having an elongated envelope with an inner wall surface wherein is contained electrodes and a shield member. The shield member has a layer of metal from the group consisting of silver and copper thereon and a portion of this layer is vapor deposited onto a designated portion of the envelope inner Wall surface.

For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claim-s in connection with the accompanying drawing in which is shown an elevation view of an electron discharge device showing the location of the metal film deposited on the envelope inner surface.

Referring to the drawing, an electron tube of the rec-tifier type adapted for use in high voltage applications has an elongated glass envelope 3 with an inner wall surface 5. The envelope 3 contains a tubular anode 7 spaced from the wall surface 5, a cathode assembly 9 within and spaced from the anode 7, a shield member 11, and a metal film 13.

The anode 7 has an innermost end 19 spaced from the shield member 11 and a top cap 15 attached to the opposite end thereof and sealed into the envelope 3 at a glass to-metal jointure 17. The top cap 15 is electrically conductive and extends beyond the jointure 17 to provide easily accessible means for applying electrical potential to the anode 7.

The shield member 11 has a central aperture 21 and rests on a mica spacer 23 having apertures 25 in longitudinal alignment with the aperture 21. A plurality of electrical conductors 27 support the mica spacer 23 with certain of the conductors 27 attached to the shield member 11. These conductors 27 are sealed into the envelope 3 at a jointure 29 and extend therethrough the provide external electrical access to the cathode assembly 9 within the anode 7. Attached to certain of the conductors 27 is a pair of rods 31 which pass through apertures 25 in the spacer 23, the aperture 21 of the shield member 11, and terminate within the anode 7 to provide support and spacing for the cathode assembly 9 attached thereto.

An annular area 33 on the surface 5 of the envelope 3 has a longitudinal termination 35 approximately immediately adjacent the innermost end 19 of the anode 7 and a second longitudinal termination 37 spaced and electrically insulated from the jointure 29. A metal film 13 covers the area 33 and tapers toward the longitudinal terminations 35 and 37 thereof.

Referring to the metal film 13, it has been found that the most critical area of electron bombardment of the envelope inner wall surface 5 is the space intermediate the shield member 11 and the innermost end 19 of the anode 7. Moreover, this area 33 is the most critical for signal radiation from the device. Thus, the metal film deposited on the wall surface 5 in the area 33 provides a barrier to bombardment of the envelope 3 as well as radiation of signals therefrom.

Further, it has been found that the longitudinal distance between the high voltage electrode and the metal film 13 has a direct relationship to the voltage at which arcing therebetween takes place. Thus, the termination 35 of the film 13 immediately adjacent the innermost end 19 of the anode 7 as distinct from films which extend beyond the innermost end 19 toward the jointure 17 whereat the voltage is applied provides a device of increased voltage capability.

Additionally, it has been found that the metal as well as the thickness and uniformity of the film 13 have an effect upon the emission and arcing capabilities of the device. Moreover, excessive heating of the electrodes and particularly the anode 7 has a deleterious etfect upon the initial emission as well as the emission capability after an extended period of use.

In a preferred process for depositing a metal film 13 on the annular area 33, numerous metals may be used and the preferred metals are those selected from the group consisting of silver and copper. These metals are economical, lend themselves to batch electroplating processes permitting ready deposition thereof on a metal surface, do not have a deleterious effect upon the emission capabilities of an eletcron discharge device, and have a high partial pressure which permits vaporization thereof in an evacuated device at reasonably low temperatures.

The metal is deposited onto the shield member 11 to provide a layer having a thickness in the range of about 30x10- to 7O 10' inches. Although other deposition methods may be used, electrodeposition is preferred because of the control of uniformity and thickness obtainable and the purity of the deposited layer. Also, layers outside of the above range may be used but it has been found that a layer less than 30X l inches presents difficulty in providing sufficient metal for a uniform film deposition while layers greater than 70 10 provide excessive metal and increase the high voltage arcing encountered during operation of the device.

Following, the structural elements which includes the shield member 11, are disposed within the envelope 3. Then, the envelope is heated, evacuated, and the structrue termionically activated in a manner common to the fabrication of electron discharge devices.

During the latter portion of the above-mentioned cycle of heating, evacuating, and activating, the shield member 11 is heated sufficiently to cause a portion of the metal layer thereon to vaporize therefrom and deposit on the adjacent annular area 33. At this time, the inner surface of the envelope 3 has been heated sufficiently to cause the removal of any gases and contaminants therefrom and is in a condition most adapted to receiving the film 13. Further, the evacuation of the envelope is such that the high partial pressure metal layer on the shield member 11 may be vaporized at a reasonably low temperature. Moreover, the cathode assembly 9 is at a temperature greater than the inner surface 5 and is therefore less attractive to the deposition of the metal vapor. Additionally, the evacuation of the envelope 3 has not been completed and any metal vapor which is not deposited on the area 33 is withdrawn from the envelope 3.

The heat may be applied to the shield member 11 in numerous ways and a preferred method is to use induction heating with RF energy. Preferably, sufficient heat is applied to the shield to vaporize enough metal therefrom to provide a film on the area 33 which is transparent and has a thickness in the range of about 0.5 X 10 to 4.0 10 inches. Although films having a thickness other than the preferred range have been tried, it has been found that films 13 having a greater thickness have increased failures due to arcing while films 13 having a thickness less than the preferred range do not provide the desired barrier to radiated signals.

Additionally, the metal vaporized from the shield memher 11 will deposit as a film 13 with a longitudinal termination substantially adjacent the innermost end 19 of the anode 7 as distinct from previous methods wherein the film 13 and top cap 15 are more closely spaced. In this manner the arcing therebetween is reduced and what has been found to be the critical radiation area, the space intermediate the shield member 11 and the innermost end 19 of the anode 7, is provided with a radiation barrier.

Referring to the previously mentioned deleterious effect on the emission capabilities of the device when heat is applied to an active electrode thereof, a series of tests was conducted on the above-described tubes. Eight groups of similar structures were processed under similar conditions. Four of the eight groups had a film provided by vaporization of a metal layer from the anode 7 and the other four groups had a film 13 provided by vaporization of a metal layer from the shield member 11. After 500 hours of testing under accelerated operational conditions, the four groups having heat applied to the anode 7 averaged about 60% effective for emission capability while the four groups having heat applied to the shield member 11 were all 100% effective for emission capability.

Additionally, four groups of similar structures were processed under similar conditions. Two of the four groups were provided with a silver film 13 on the area 33 by vaporizing a portion of the metal layer from the shield member 11 while the remaining two groups had no film deposition. The two groups with the silver film had no failures for diodehausen while the two groups without the silver film had and failures when tested in the same television set.

Thus, there has been provided an electron tube adapted for use in high voltage applications having a more effective barrier to signal radiation and envelope electron bombardment than any of the known devices. Further, the process for depositing the film on the envelope surface permits the location thereof such that applied voltage values may be increased and arcing to the film reduced. Moreover, the process for depositing the film by heating the shield rather than an active electrode extends the period of useful operation of the device. Also, the process is economical and the actual film deposition requires neither additional processes nor handling.

While there has been shown and described what is at present considered the preferred embodiment of the invention, it will the obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention as defined by the appended claims.

What is claimed is:

1. An electron discharge device adapted for use in high voltage rectifier applications comprising:

an elongated cylindrical envelope having an inner wall surface and containing a shield member and electrodes including a tubular anode having an innermost end, said shield member supported and spaced by electrical conductors sealed into one end of said envelope and said anode supported and spaced by an attached top cap sealed into the opposite end of said envelope, said inner wall surface having an annular area with longitudinal terminations immediately adjacent said anode innermost end and spaced from said electrical conductor and envelope seal, and

a film of metal from the group consisting of silver and copper deposited on said annular area.

2. An electron discharge device adapted for use in high voltage rectifier applications comprising:

an elongated cylindrical glass envelope having an inner wall surface and containing a shield member longitudinally spaced from the innermost end of a tubular anode, said inner wall surface having an annular area immediately adjacent the longitudinal space intermediate said innermost end and said shield memher, and

a film of metal from the group consisting of silver and 5 6 copper deposited on said annular area, said film hava radiation barrier film of a metal selected from the ing a thickness in the range of about 0.5)(10 to metal group consisting of copper and silver deposited 4.0 10 on said annular area, said film being transparent and 3. An electron discharge device adapted for use in high having a thickness in the range of about 0.5 X 10- voltage rectifier applications comprising: 5 to 4.0 10- inches.

an elongated glass envelope having an inner wall surface and containing a shield member and electrodes in- References Cited by the Examiner eluding a cathode assembly within said shield mem- UNITED STATES PATENTS her and a tubular anode having an innermost end,

Said Shield member being supported and longitudinal- 10 l "$13 5 ly located by attached electrical conductors sealed 1 1 1 5 W et a into one end of said envelope and s id anode b i 3, 5 1 19 7 Relchert 313-l78 supported and spaced from said shield member by 2,877,143 Ga p 117-227 a top cap sealed into the opposite end of said en- 2,933,633 4/196 P a1 313178 X velope, aid inner wall surface having an annul r 15 1 3/1952 G llup 313-178 area with a first longitudinal termination immedi- 3,041,126 6/1962 Splcel' et 6-9 ately adjacent said anode innermost end and a sec- 0nd longitudinal termination intermediate and adja- JOHN HUCKERT Pnmary Exammer' cent said shield member and said conductor envelope JAMES D. KALLAM, DAVID J. GAVIN, Examiners. seal; and 20 

3. AN ELECTRON DISCHARGE DEVICE ADAPTED FOR USE IN HIGH VOLTAGE RECTIFIER APPLICATIONS COMPRISING: AN ELONGATED GLASS ENVELOPE HAVING AN INNER WALL SURFACE AND CONTAINING A SHIELD MEMBER AND ELECTRODES INCLUDING A CATHODE ASSEMBLY WITHIN SAID SHIELD MEMBER AND A TUBULAR ANODE HAVING AN INNERMOST END, SAID SHIELD MEMBER BEIN GSUPPORTED AND LONGITUDINALLY LOCATED BY ATTACHED ELECTRICAL CONDUCTORS SEALED INTO ONE END OF SAID ENVELOPE AND SAID ANODE BEING SUPPORTED AND SPACED FROM SAID SHIELD MEMBER BY A TOP CAP SEALED INTO THE OPPOSITE END OF SAID ENVELOPE, SAID INER WALL SURFACE HAVING AN ANNULAR AREA WITH A FIRST LONGITUDINAL TERMINATION IMMEDIATELY ADJACENT SAID ANODE INNERMOST END AND A SECOND LONGITUDINAL TERMINATION INTERMEDIATE AND ADJACENT SAID SHIELD MEMBER AND SAID CONDUCTOR ENVELOPE SEAL; AND A RADIATION BARRIER FILM OF A MELTED SELECTED FROM THE METAL GROUP CONSISTING OF COPPER AND SILVER DEPOSITED ON SAID ANNULAR AREA, SAID FILM BEING TRANSPARENT AND HAVING A THICKNESS IN THE RANGE OF ABOUT 0.5X10-6 TO 4.0X10-6 INCHES. 